added support for Model migrations

now we have a table core.migration and each model (User, Group, Item, ItemContent and a new Migration) have its own
row in the table with a version number

added to config:
db_make_migration_if_needed and db_stop_if_migration_fails (need description yet)

winixd/models/item.h

@@ -175,17 +175,20 @@ public:
 	 */
 
 
-	/*
-	 * temporary
-	 */
-	void do_migration(morm::ModelConnector * model_connector, Log & log);
+	bool do_migration(int & current_table_version);
 
 	void propagate_connector();
 
+
+
 protected:
 
 	CalcItemsHelper calc_items_by_url(long parent_id, const std::wstring & url);
 
+	bool do_migration_to_1();
+	bool do_migration_to_2();
+	bool do_migration_to_3();
+	bool do_migration_to_4();
 
 };